1. Field of the Invention
This invention relates generally to clamping apparatus, and more particularly relates to new and improved clamping apparatus for clamping the ends of the strings of a game ball racket in the frame of the racket with non-uniform clamping pressure to reduce the tendency of the strings to yield or rupture along their clamped lengths due to the combination of the clamping pressure and the tensile stress produced in the clamped lengths of string due to stringing and racket play.
2. Description of the Prior Art
As is known to those skilled in the art, and as disclosed in British specification No. 23,260 date of application Oct. 31, 1908; British specification No. 887,526 date of application Dec. 19, 1958; and U.S. Pat. No. 3,994,495; clamping apparatus have been used to clamp the ends of individual game ball strings to the frame of the game ball racket. Such clamping apparatus, for example as disclosed in U.S. Pat. No. 3,994,495 includes a pair of opposed tapered wedges or ferrule halves for being wedgingly received within a tapered passageway formed in the frame of the game ball racket to clamp the end of a game ball string to the racket frame.
As is further known to those skilled in the art, such prior art clamping apparatus apply uniform clamping pressure along the clamped length of the string, and as is still further known to those skilled in the art, game ball strings clamped by such prior art clamping apparatus have a tendency to rupture at the point where such strings exit the clamping apparatus, which critical point is referred to herein as the pulled or forward end of the clamped length of the string.
Further, and as is also known to those skilled in the art, upon the game ball string being clamped tensile stress is produced in the clamped length of the string due to stringing and due to the string impacting with a game ball during racket play. Such tensile stress produced in the clamped length of the string decreases from a maximum at the forward or pulled end of the clamped length of the string to a minimum at the rearward or free end of the clamped length of string.
As is still further known to those skilled in the art, a significant factor in determining whether or not a member in stress, such as the clamped length of the string, will yield or rupture, is the equivalent (combined) stress which is a function of the tensile stress and the compressional stress produced in the member at each point therealong. Thus, it will be understood that the equivalent stress in the clamped length of the string will be maximum at the forward or pulled end of the clamped length of string where the tensile stress is maximum and where the compressional stress produced in the clamped length of string is also high due to the uniform clamping pressure which causes the compressional stress to be of a uniform maximum value along the entire clamped length of string. It is believed, as is taught in detail below, that it is the combined effect of the maximum tensile stress and high compressional stress present at the forward or pulled end of the clamped length of string which causes the tendency of the string to rupture at this critical point.